Brazilian officials sent 1,200 extra police into the streets of Rio de Janeiro on Tuesday to halt an upsurge of roadblocks and mass robberies by gangs that they say are challenging police for control of slums.

The military-run police announced they had ordered the officers off of desk work and into the streets to quell the attacks that have renewed concerns about security for the 2014 World Cup and 2016 Olympics.

Rio has been hit by a spike in violence since Sunday, with at least five mass robberies of motorists on key highways, including the one leading to the international airport.

Witnesses say the armed men have blocked roadways with cars, then moved down the line of trapped vehicles, yanking people from their cars and robbing them in broad daylight. One man who resisted was shot to death in a poor area of northern Rio, police said.

Suspected drug gang members, armed with assault rifles, pistols and even grenades, have tossed molotov cocktails into several of the cars after motorists fled.

Burned-out husks of the cars littered the sides of roads in several parts of the city, including wealthier areas that are usually spared the rampant violence that permeates the city's slums.

Police responded by deploying riot officers on expressways into the city of 6 million people and sending patrols into 16 gang-controlled shantytowns to hunt down gang members they hold responsible for the attacks.

Officers seized drugs, cells phones and various weapons, including a Kalashnikov in the action. Two men died confrontations with police Tuesday, officials said. Eleven have been arrested.

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Rio state Public Safety Director Jose Beltrame, in charge of the security forces, said the attackers are trying to disrupt a city campaign to push gangs out of key shantytowns.

"There are groups of criminals who have been installed here for 20, 30 years, and they might not want to give up. But we're not giving up either," he said. "If they keep this up, we'll redouble our efforts. Anyone who gets in our path will be run over."

He said eight high-level drug traffickers are suspected of coordinating the attacks from local prisons and asked they be moved to more distant federal penitentiaries.

Thirteen shantytowns have been pacified over the past two years. The plan is to free 40 — a small fraction of Rio's more than 1,000 slums — of gang control by the time of soccer's World Cup.

The national minister of justice, Luiz Paulo Barreto, assured executives of soccer's governing body, FIFA, on Tuesday that the country is preparing to welcome the games in a climate of "peace and tranquility."

City officials also sought to reassure residents of Rio's dangerous slums.

"People might be scared, but we have a purpose here," Beltrame said. "We are living for now with the problems of the old Rio. They don't go away magically. But we are working toward a definitive solution."

Taxi driver Leonard Viera de Oliveira, 40, took little comfort. Criminals used to just rob you, he said. Now they're burning your car and blocking the road.

He gestured at police officers on the side of the road: "They're here now, but how long can they keep it up? I'm out there until 4 a.m., and if I need them, will they be around?"